Conventionally, as a part to be mounted on a board, there has been used one as shown in FIG. 1 (here, as an example, a discharge gap element is given).
Referring to FIG. 1, reference numeral 12 denotes a board, reference numerals 12a and 12b mounting holes on the board 12. Reference numeral 15 denotes a discharge gap element, and reference numerals 15a, 15b leads projected from the side of an electrode on both ends of the discharge gap element 15. The discharge gap element 15 is mounted on the board 12 by inserting these leads 15a, 15b into the inserting holes 12a, 12b on the board 12 and then by soldering them.
As an example of a mounted part other than the discharge gap element, JP 82933/1993 A disclosed one in which a sub-board is mounted on the upper surface of a mounting board and a leadless part is soldered onto this sub-board.
Since this conventional discharge gap element is mounted into the mounting holes on the board as shown in FIG. 1, it is mounted on the upper part of the board and the height of the board after mounting obtained by an equation (the thickness of the board itself+the height of the discharge gap element element). In order to hold down the height of the board, there has no other choice but to lower the height of the discharge gap element. The same holds true for the other parts to be mounted on the board, as they are mounted on the upper part of the board, there has no other way than to lower the height of the part in order to hold down the height of the board.
In addition, the conventional discharge gap element was permitted to arrange only in the neighborhood of the mounting holes on the board and to have a lower freedom of arrangement thereof. For this reason, in case of trying to hold down the height of a specific portion of the board after parts have been mounted thereon, if the necessity arises to move the position of the discharge gap element on the board, much time requires for redesign of the circuit pattern.
Further, the discharge gap element has conventionally been used in a lighting device for a discharge lamp of a motor vehicle, or the like.
First, the conventional discharge lamp will be described.
Among the discharge lamps, a high intensity discharge (HID) lamp such as a metal halide lamp, a high-pressure sodium vapor lamp, a mercury lamp, or the like, has advantages that it has large luminous flux, high lamp efficiency, and long lifetime. Therefore, it has been used as an illumination lamp in indoor and outdoor facilities, warehouses, factories, or the like, or as a street lamp, or the like. Recently, it is being used particularly as a headlamp for a vehicle such as a motor vehicle. In order to light this kind of discharge lamp, it is necessary to apply a high starting voltage at the time of starting. In addition to a stabilizer to stably light the discharge lamp, a starting device (an ignitor) to generate the starting voltage, including parts called as a transformer, a capacitor, a discharge gap element, or the like, is required.
FIG. 2 is a longitudinal sectional view of the lighting device as seen from the vehicle explaining a conventional lighting device for the HID headlamp of a motor vehicle.
Inside a housing 1 a reflector 2 is attached which acts as a reflecting mirror to converge an optical axis, and on an inner surface of which a reflecting surface is coated. An HID bulb 4 held by a bulb socket 3 is mounted substantially in the center of the reflector 2. An ignitor 5 for generating a high voltage, e.g., of 30 KV in order to light the HID bulb 4 is disposed separate from the HID lighting fixture. A power control circuit (ballast) 7 for lighting the HID lighting device is disposed integrally with, or separate from, the ignitor 5 or a transformer 6. The HID lighting device configured in this manner instantaneously applies a high voltage to the HID bulb 4 to induce the high-voltage discharge of the HID bulb, whereby the gas filled inside the bulb gives rise to discharge to light it. Reference numeral 8 denotes a lens and the luminous flux of the HID bulb is dispersed within a predetermined range through the lens 8 to illuminate the ahead of the vehicle, thereby securing the safety of the vehicle when running in the dark.
This kind of HID headlamp is mounted in a space between a bumper 9 and an engine hood 10. In the primitive HID lighting device, the ignitor 5 for generating the high voltage and the control circuit (ballast) 7 for supplying electricity to the HID lighting device are mounted separate from the lighting fixture, and the power is supplied to the bulb socket 3 through a harness 11.
In this kind of structure, since the ignitor 5 and the bulb socket 3 are disposed separate from each other and they are connected through the harness 11, it was compelled to cover the harness 11 with a high-performance electromagnetic shielding wire in order to shield the electric waves to be leaked out from the harness 11. However, complete removing of the effect on a car radio or the like was ended in failure.
In order to solve this problem, the best way is to incorporate the high-voltage module inside the lighting fixture and also to shield the inside of the lighting fixture from the electromagnetic waves by means of metallic thin film deposition or the like. As one approach, it is devised that the ignitor 5 for generating the high voltage is integrally mounted with the HID bulb.
One such example will be described with reference to FIG. 3.
As shown in FIG. 3, it has conventionally been known (e.g., in JP 136938/1991 A) to annex the ignitor 5 on a board on which the HID bulb 4 is mounted, and to house them inside the lighting fixture.
Referring to FIG. 3, reference numeral 12 denotes the board which is attached to the reflector 2 and onto which the HID bulb 4 is assembled, reference numeral 13 a transformer around which a primary coil and a secondary coil are wound to generate the starting voltage for the HID bulb, reference numeral 14 a charging capacitor therein the starting energy, reference numeral 15 a discharge gap element. Through a potential difference charged in the capacitor 14 on both ends of the discharge gap element 15, the gas filled inside the part quickly starts electric discharge due to dielectric breakdown, which supplies electricity to the primary coil of the transformer 13. This generates a high-voltage pulse of 20 KV through 30 KV in the secondary coil of the transformer 13, whereby the HID bulb 4 is illuminated by discharge. Reference numeral 16 denotes a cap.
Typically, a starting device 300 of the HID lighting device is made up of the transformer 12, the capacitor 14, the discharging gap 15, or the like. The one described with reference to FIG. 3 houses the starting device 300 inside the lighting fixture. In order to prevent the electric noises from being leaked out, the inner wall surface of the housing 1 is provided with a coating of a metallic thin film for shielding purpose, and the body of the housing 1 is grounded.
As a discharging gap 15, the same one is used as that described with reference to FIG. 1.
However, such the arrangement as shown in FIG. 3 encumbers miniaturization, in particular, thickening of the starting device 300, as the starting device 300 is housed inside the lighting fixture. It is therefore infeasible to miniaturize the lighting fixture and to attain a space efficiency inside the vehicle. Further, soldering after the leads 15a, 15b extended from both electrodes of the discharge gap element 15 have been inserted into the board requires the cutting work for excess leads protruded from the back of the board. In addition, the discharge gap element 15 bent at the lead wires interferes with other parts on the board.
Further, as described above, the parts such as the conventional discharge gap element, or the like, are mounted on the upper part, of the board, when they are mounted on the mounting board. Therefore, in order to hold down the height of the board, there has no other way than to lower the height of the parts.
Still further, in the mounting board on which the parts such as the conventional discharge gap element, or the like are mounted, the parts were allowed to arrange only in the vicinity of the mounting holes on the board and to have a lower freedom of arrangement. Therefore, in case of trying to lower the height of a particular portion of the board after parts have been mounted thereon, if the necessity arises to move the position of the discharge gap element on the board, much labor costs for redesign of the circuit pattern.
This invention has been made to solve the above and other problems and an object thereof is to provide a mounting board suitable for miniaturization of the apparatus as well for mass production, a board for mounting thereon a part, a method of mounting the mounting board, as well as a bulb socket using the mounting board.